pH pen case design



FIG. 1 is a top and right side perspective view of a pH pen case design showing my new design;

FIG. 2 is a left side elevational view thereof, the right side is a mirror image thereof;

FIG. 3 is a front plan view thereof; and,

FIG. 4 is a rear plan view thereof. 

The ornamental design for a pH pen case design, as shown and described. 